Overcurrent protection structure and method and apparatus for making the same

Abstract

The overcurrent protection structure according to the present invention mainly comprises a fusible fuse structure unit disposed in a coating, and the both ends of the fusible fuse structure unit extend outwardly beyond the coating and form a first electrode and a second electrode. In the manufacturing process, the gas-assisted injection molding process enables at least one space for accommodating gas disposed between the fusible fuse structure unit and the coating such that the heat generated by the electrically energized the fusible fuse structure unit will not dissipate through the heat conduction of the coating in order to ensure that it will blow at high temperature when reaching a specific current or a specific temperature and the circuit protection effect.

1. An overcurrent protection structure comprising:
 a coating made of an arc resistant material comprising a thermoplastic material or a thermosetting material, the arc resistant material further being filled with magnesium hydroxide dihydrate such that the coating absorbs heat and releases water of crystallization until a temperature in excess of a lead-free solder melting point is reached; 
 a fusible fuse structure unit, which is encapsulated by the coating, wherein a gas filled space exists between the fusible fuse structure unit and the coating, the gas filled space extending along at least a full length of the fusible fuse structure unit, such that the fusible fuse structure makes no direct contact with the coating to prevent the heat generated by the fusible fuse structure unit from dissipating through the gas filled space to the coating; and 
 a first electrode and a second electrode, which are respectively lead-free soldered to both ends of the fusible fuse structure unit and extend outwardly beyond the coating. 
 
     
     
       2. The overcurrent protection structure as claimed in  claim 1 , wherein the coating is formed with two layers comprising an inner layer made of the arc resistant material and an outer layer made of coating material. 
     
     
       3. The overcurrent protection structure as claimed in  claim 1 , wherein the outside of the fusible fuse structure unit is further coated with a thermal insulating material with arc resistance. 
     
     
       4. The overcurrent protection structure as claimed in  claim 1 , wherein the first electrode and the second electrode are formed by lead frame stamping. 
     
     
       5. The overcurrent protection structure as claimed in  claim 1 , wherein the space is further filled with an inert gas. 
     
     
       6. The overcurrent protection structure as claimed in  claim 5 , wherein the coating and the gas in the space are molded by gas-assisted injection. 
     
     
       7. The overcurrent protection structure as claimed of  claim 1 , wherein the coating absorbs heat and releases water of crystallization until a temperature of 340 Celsius is reached.